Many of nature’s workers help farmers around the globe to provide an adequate supply of food to the growing global population: honey bees and other pollinating insects are indispensable to agriculture, but they are impacted by a ­number of negative factors. Bayer experts are working to improve the health of these busy insects, both inside the beehives and out in the field.

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Challenge: Honey bees and other pollinating insects help to secure our food supply. But they are impacted by a number of negative factors.

Solution: Bayer researchers are working on ways to help these animals, for instance by providing tools to fight parasites and diseases inside honey bee hives.

Bees may be tiny, but their contribution is tremendous: together with other animals like birds and bats, insects such as honey and wild bees, flies, beetles and butterflies pollinate about one third of all crops worldwide. These busy farm-hands make sure that high-quality fruits and vegtables grow in plantations around the world. Apple trees, for instance, produce significantly higher yields when their pollen is transported by insects and farmers do not need to rely on the wind. “Without the assistance of these animals, almond trees, pumpkin vines and melon plants would only produce very few, low-quality fruits,” explains Dr. Christian Maus, Global Pollinator Safety Manager at the Bayer Bee Care Center. Experts estimate that the economic value of animal pollination worldwide amounts to more than EUR 150 billion a year.

Dr. Klemens Krieger knows all about life inside the hive and also understands the bee’s greatest enemy, the Varroa mite. He is also collaborating with external partners to find effective ways of controlling this parasite.

The Biggest Enemy for Bees is Barely a ­Millimeter Long: Varroa Destructor

The western honey bee (Apis mellifera) contributes a major share of this service. In the United States, for instance, honey bees are used specifically to pollinate almond trees: some 1.7 million bee colonies with up to 50,000 insects per colony buzz through almond plantations every year – over half of all the bee colonies in the entire country. “Honey bees have become important livestock worldwide,” Maus points out. But these avid fliers are at risk. Their greatest enemy is barely a millimeter long, but it is annihilating entire bee colonies around the world: Varroa destructor is the name of the mite that attaches to bees and feeds on their hemolymph. The parasite not only severely weakens bees, it also frequently transmits deadly infectious diseases. “The Varroa mite originated in Asia, where it is a natural parasite on the eastern honey bee (Apis cerana). However, since it started infesting the western honey bee, it has spread over almost the entire globe,” explains Dr. Klemens Krieger of Bayer HealthCare‘s Animal Health Division, who is responsible for bee health among other duties. “The only significant place it hasn‘t spread to yet is Australia.”

Destructive Mite

Mites of the species Varroa destructor only infest honey bee colonies. Outside the breeding cycle, female mites cling on the hard outer shell of adult bees, crawling to the soft, intersegmental tissue and puncturing a hole there to feed on hemolymph, a blood-like liquid. In the process, the mites transmit harmful microorganisms, such as deformed wing virus (DWV). Bees with this disease have stubby wings and are unable to fly. The mites multiply rapidly in the closed brood cells of a bee hive. Shortly before the bees cap the cells with wax, the female mites enter the cell, hide under the bee larvae, feed on their hemolymph and lay their eggs on the floor of the cells. In the case of severe DWV infection, the bees often die before hatching, which threatens the survival of the entire colony.

The only significant place the Varroa mite hasn‘t spread to yet is Australia.

Beekeepers have relatively few means of controlling the parasite. “Our arsenal includes organic acids, essential oils and synthetic active substances called acaricides. Used properly, they kill the mites without affecting the bees or contaminating the honey,” Krieger explains. Developing these highly specific acaricides is a major challenge for research and development (R&D) experts, however, which explains why only a few active substances are currently approved for treating honey bees. “This is why we have to use them as efficiently and responsibly as possible. That means alternating between substances with different mechanisms of action,” ­Krieger says. This method is the only way to prevent the selection of mite strains that are resistant to a specific active substance. “But many beekeepers underestimate the risk of resistance development,” Krieger says. Even if beekeepers treat their colonies against Varroa mites successfully, resistant parasites may survive the treatment. If they are not eradicated by a different active substance, they can multiply unchecked in the hive and create a resistant population. What’s more, the bees constantly transport the pest into other hives, helping it to spread. “Until we have bees that are resistant to mites, it is extremely important for beekeepers to repeatedly check how severely a hive has been infected with Varroa. It is the only way they can effectively adjust their mite control activities and keep infestation under the damage threshold,” says Krieger

2,000

Varroa mites can kill a colony of 30,000 honeybees.

The Varroa mite originated in Asia, but has since spread towards the west and now threatens the western honey bee almost all over the planet. Only Australia has managed to keep the parasite at bay to date.

Bayer experts are investigating mite DNA, looking for natural mutations that make the parasites resistant to common acaricides. A minute change can alter the site of action enough that an active substance no longer works and becomes entirely ineffective at controlling mites. Krieger and his colleagues are therefore collaborating closely with Rothamsted Research in the United Kingdom. “We must first understand the mechanisms underlying resistance, so that we can control the parasite in the long term,” explains Martin Williamson, Senior Scientist at ­Rothamsted Research.

We must first understand the mechanisms underlying resistance, so that we can control the parasite in the long term.

Martin Williamson, Senior Scientist at Rothamsted Research

DNA Testing: Developing Simple Methods to Detect Resistant Mites

Williamson’s team has already identified how specific mites have adapted to pyrethroids, one group of acaricidal active substances. On this basis, they then developed a molecular biological test which shows if a mite is pyrethroid-resistant. Now they want to team up with Bayer researchers and do the same for other acaricides. “Our goal is to develop fast, simple and cheap methods for detecting all resistance types,” Krieger explains. Beekeepers would then be able to determine if the mites in their hive are resistant and if so to which agents, and could then select the most effective treatment.

Focus on bees: the diligent work of beekeepers is not the only factor that has an impact on bee health. The weather also plays an important role, and agricultural practices are also a relevant factor

crop protection products are frequently accused of causing harm to honey bees. Conscientious Bayer experts are therefore constantly working to make these products and the technology used to apply them even safer.

An initial and very practical test method has already been developed by the Bayer bee experts in partnership with Dr. Ralph Büchler, Head of the Kirchhain Bee Institute in Germany: the Varroa Diagnosis Box. The beekeeper fills this hand-sized box with about 500 live bees from the hive and then closes the opening with a feed paste and gives them about six hours to eat their way through the seal to freedom. During this time, an acaricidal active substance kills any mites inside the box. They can be seen afterwards, stuck to the bottom. From this number, the beekeeper can then calculate the approximate number of mites in the hive and determine the degree of risk to his colonies. R&D experts are currently testing their innovation under different climatic and beekeeping conditions. “We are considering using the box to diagnose resistances as well, which could well be viable if we use different active substances,” Krieger says. Beekeepers would then have a simple method on hand to test hives directly, determine if they are infested with resistant mites, and combat the pests at the same time.

Nature's Weapon

Formic acid is evaporated inside a hive; the vapor poisons the parasites. Nature also makes use of this acid. Some ant families, from which the acid was first extracted, use this corrosive liquid as a defense, spraying it onto their predators. Other animals, such as jellyfish and beetles, likewise use the substance for defense. Even plants take advantage of it: the irritating bristles on stinging nettles are filled with formic acid.

However, the Varroa mite is not the only threat to the health of honey bees: the weather as well as beekeeping and farming practices also determine how honey bees and other pollinators fare.

Controversy Surrounding Neonicotinoids in the European Union

The use of crop protection products has frequently been a particularly controversial issue in the general debate surrounding this topic. The focus in most cases is on a group of pesticides called neonicotinoids, some of which are applied as a protective layer on, for example, oilseed rape, corn and soybean seeds in a process experts call seed treatment. The systemic active ingredients of these products protect seeds and young plants against voracious insects and take effect after germination, working from the inside. “Seed treatment is essential for many crops,” explains Dr. Reinhard Friessleben, Head of Application Technology at Bayer CropScience. The chemicals protect oilseed rape, for instance, against the ravenous cabbage flea beetle, and eliminate the wireworms that chew on the roots of corn. However, the product needs to adhere well enough to the seeds. If the agent is partly rubbed off the seeds during planting, it is difficult to totally avoid emission of the resultant dust into the environment, as happened during the 2008 corn-planting season in several regions of Germany. The dust settled on other flowering plants in the vicinity of the fields. “That can be harmful to pollinating insects feeding on these other plants,” explains Bayer researcher Friessleben. High-quality seed treatment generates significantly less dust. Many scientific studies, field observation data and risk assessments show that, under realistic conditions, neonicotinoids are not harmful to bee colonies when used as directed and according to best practice. The European Union nevertheless restricted the use of some neonicotinoids, to the dismay of farmers (see box on page 41), who lost a critical agent for protecting crops against pests. And virtually no effective alternatives exist.

Brief History of ­Neonicotinoids

Neonicotinoids came onto the market in the 1990s. For farmers they were a welcome alternative to other compounds, against which many pest insects had become resistant. But a damper was put on this success in late 2013: the European Commission imposed major restrictions on the use of some compounds in this group, claiming that harmful effects of the active substances on bees could not be ruled out. This issue is the subject of controversy around the world. However, numerous scientific studies have come to the conclusion that no relationship exists between the use of neonicotinoids and the decline of honey bees.

Bayer researchers are continuously looking for new ways to make seed treatments even safer, and protect both beneficial insects and the environment. Experts from Bayer CropScience and Bayer Technology Services are collaborating closely on a project called ‘Zero’ Dust. Their goal is to further reduce dust generation and emissions when planting treated seed. The project name ­‘Zero’ Dust does not mean that there will be no dust emissions at all, but rather refers to all measures that can help to minimize the generation and emission of dust. The researchers and developers are examining the entire process, from the makeup of the active substances and additives in the treatment layer, to the planting of the seeds on the field. In one sub-project, agricultural experts and engineers are developing a kind of vacuum cleaner for corn planting. “When handling and planting treated seed, dust can be abraded. This dust is extracted from the air, transported to the ground and buried there,” explains Dr. Lubos Vrbka of Environmental Modelling at Bayer CropScience. The heart of the technology is a unit known as a cyclone separator: it sucks the exhaust air pertinent to the pneumatic working principle from the sowing machine, and with it the dust from the potentially abraded seed treatment agent and any dirt kicked up in the sowing process. This air/particle mixture is blown into the cyclone, where centrifugal force causes the dust particles to strike the inside wall of the cyclone container. From there they fall into a hopper and are buried underground. The clean air is released close to the ground.

SweepAir helps to ensure that seed treatment agents do not escape into the atmosphere. The system separates the sowing machinery’s exhaust air, blowing the air/dust mixture into a cyclone where centrifugal force causes the dust particles to strike the inside wall of the cyclone container. From there they fall into a hopper and are then buried underground like the seeds.

The SweepAir prototype has been installed on conventional corn planting machinery for field studies.

Interview: Martin Williamson

“We Need Different Modes of Action”

Martin Williamson is a molecular biologist and Senior Scientist in the Biological Chemistry and Crop Protection Department of Rothamsted Research in the United Kingdom. research spoke to him about the danger of resistance in parasites.

How does resistance evolve in parasites?

Resistance is usually caused by simple point mutations that occur naturally in all organisms at extremely low frequencies; however, when the mutation occurs in the target receptor for a pesticide, for example, then that individual may be more likely to survive subsequent treatments. The genetic changes are passed from one generation to the next and further selection with the pesticide can quickly result in a fully resistant population.

What are the challenges in detecting the underlying mechanisms?

Resistance is normally caused by two different types of mechanism. We have a good knowledge of both types from work that has been done on a range of insect and mite pests. The main challenge in Varroa mites is to obtain a range of samples with well-characterized resistance on which we can identify the mechanisms involved.

How can we tackle the resistance problem in the Varroa mite?

The key to effective resistance management is to have compounds with different modes of action. They can be rotated regularly to prevent resistance to any particular compound. Of course, this is not always so simple. For Varroa mite control there are only a few active compounds, and resistance is already known for each of these. We need to manage the resistance more effectively by understanding the underlying mechanisms and then by developing rapid assays. In this way, it should be possible to predict which type of resistance is present and to make informed recommendations as to the most effective treatment in a particular group of hives or region.

Positive Reception from Farmers and Equipment Manufacturers

SweepAir is the name given by the Bayer experts to their field vacuum cleaner, which farmers in Italy and Germany have already tested successfully in field trials. The researchers did encounter difficulties, however: for example, the fine, electrically charged dust adhered to the inside wall of the cyclone. But engineers from Bayer Technology Services found a solution. “We installed a shaker that vibrates the container automatically every few seconds. This loosens the dust so that it drops downwards,” explains Dr. Volker Michele, a fluid dynamics expert at Bayer Technology Services.

The SweepAir system has also passed a test at the distinguished Julius Kühn Institute, where experts compare seed-sowing machine systems with a reference machine that blows air and dust upwards. Compared to such reference machines, SweepAir releases 99 percent less dust into the atmosphere. European farmers have high hopes for the new technology. “They have been waiting for a solution that enables an optimized risk management for seed treatment products, which is expected to positively influence the perspectives for using neonicotinoids again,” Vrbka says. The Bayer specialists have already received positive feedback from farmers and equipment manufacturers. Their next task is to transfer the technology to machine manufacturers, who could then produce and market the corresponding equipment. “An important next step will now be to attain the endorsement of government authorities for the use of these devices, and their support for the new technologies as an optimized tool that assures the safe use of neonicotinoid seed treatment,” Friessleben explains.